This invention generally relates to apparatus and method for forming an airlaid fibrous article. The fibrous article can be a fibrous web which can be employed to produce an absorbent pad for applications such as disposable diapers, child""s training pants, feminine care articles, incontinence articles, and the like.
In the general practice of forming fibrous web materials, such as laid fibrous articles, it has been common to utilize a fibrous sheet of cellulosic or other suitable absorbent material which has been fiberized in a conventional fiberizer, or other shredding or comminuting device, to form discrete fibers. In addition, particles of superabsorbent material have been mixed with the fibers. The fibers and superabsorbent particles have then been entrained in an air stream and directed to a foraminous forming surface upon which the fibers and superabsorbent particles have been deposited to form an absorbent fibrous web.
The forming surfaces utilized in such systems have been constructed with a wire or screen grid and can typically employ a pneumatic flow mechanism, such as vacuum suction apparatus, to define a differential pressure zone on the forming surface and impose a pressure differential thereon. The pressure difference has typically provided an airflow through the openings or perforations in the screen or grid of the forming surface. The use of vacuum suction to draw the air-entrained fiber stream onto the forming surface, and pass the airflow through the forming surface has been employed in high-speed commercial operations.
The prior practice of forming airlaid fibrous webs has also employed various mechanisms to produce gradations in basis weight along the fibrous webs. For example, the conventional devices have been employed to produce gradations of basis weight along a longitudinal direction of the formed web, i.e., in the direction of movement of the fibrous web through the forming process. Conventional devices have also been employed to provide basis weight variations along a transverse, cross-direction of the formed web.
Conventional vacuum-deposition systems, such as those described above, have continued to exhibit various shortcomings. For example, with the conventional devices, it has been difficult to form airlaid fibrous webs having large changes in basis weight. In particular, the forming surfaces have been constructed to include depressions or pocket regions that have been configured for the formation of the desired high-basis-weights in the formed fibrous web. Where the pocket regions have been large and deep, it has been difficult to direct desired amounts of fiber material into the pocket regions. The conventional techniques have also produced excessively large variations in the distribution of web material along the final, free-surface of the laid fibrous web. As a result, further processing has been required to remove or otherwise redistribute large amounts of the web material. Such redistribution equipment and processes have been difficult to operate and maintain. Accordingly, it would be a substantial advance in the art to provide a method and apparatus which can provide a more reliable and more efficient forming of desired, high-basis-weight regions in an airlaid fibrous web.
An apparatus for forming a fibrous web includes a movable, foraminous forming surface and a vacuum-commutator duct system which is located substantially subjacent the forming surface. The vacuum-commutator duct system has an entrance opening that changes in configuration along a longitudinal dimension of the entrance opening.
In a process aspect, a method for forming a fibrous web includes a moving of a foraminous forming surface, and a locating of a vacuum-commutator duct system at a position which is substantially subjacent the forming surface. The vacuum-commutator duct system is configured to have an entrance opening that changes in shape along a longitudinal dimension of the entrance opening.
In a desired aspect, the vacuum-commutator duct system can be substantially stationary. In another aspect, the movable forming surface can include a system of baffles that are arranged to cooperate with the vacuum-commutator duct system.
In its various aspects and features, the present invention can more effectively direct the desired web material directed into appointed, higher-basis-weight sections of the selected forming surface. Additionally, the technique of the invention can better provide a laid web that has less troublesome variations in depth contour along a substantially terminal, free-surface of the formed web. As a result, the desired distributions of web basis weight can be formed with less rearrangement or redistribution of the laid web material. Accordingly, the various features and aspects of the invention can help provide a forming system that can be more effective and reliable, and can operate with less maintenance.